Incubators are typically used for growing cultures in a controlled environment wherein both temperature and atmospheric gas concentration are maintained at selected levels. For certain applications it is highly desirable to have both temperature and gas concentrations maintained within strict tolerances while still allowing easy access to the incubator chamber for adding or removing items to and from the chamber or for inspecting the contents of the chamber. Control of environmental variables is desirable to maintain accuracy and reproducability of incubation results. Typical incubators have used either open-coil heaters within the incubator chamber or water jackets surrounding the incubator chamber wherein the water jacket is heated and heat is transferred to the chamber. However, while such configurations can be effective in heating an incubator, they do not necessarily provide as strict a control on the incubator temperature as is desirable for consistent results.
Conventional air heater type incubators lack the temperature stability of the water jacket type. However, according to prior water jacket technology, water jacket temperature is regulated at the desired incubator internal temperature, and opening the door will cause the air temperature to drop rapidly until the door is closed whereupon the temperature begins to recover. The rate of recovery is proportional to the difference in water jacket and the internal air temperature, with recovery slowing as the air temperature approaches the water jacket temperature. A typical full recovery requires approximately forty minutes. If the door is opened more than once every forty minutes, the desired operating temperature would never be attained. Moreover, over-controlling the temperature of the water jacket can cause excessive overshoot because of the delayed response of the water jacket to applied heat.
Therefore, it would be desirable to provide an incubator having more accurate temperature control.